This invention relates to castor assemblies and to housings fitted with castor assemblies, particularly, but not exclusively, housings used to house electronic equipment.
Castors are often fitted to housings to enable them to be wheeled into a position of use where they may be jacked off the castors and supported on feet, some or all of which can be made adjustable for levelling of the housing and/or to provide the jacking facility.
In our European patent application no. EP 99300078.5 dated Jan. 6, 1999, we have described a support means for a housing comprising, a each of a plurality of positions, a wheel and a foot provided together on a single mounting. The exemplary castor assembly comprises a castor body which is pivotable about the axis of a castor pin the projecting upper end of which is adapted to be received in a vertical bore in the underside of a housing base, and the castor body is provided with a threaded vertical bore, spaced horizontally from the castor pin axis and on the opposite side of the castor pin axis from the rotational axis of the castor wheels carried by the body, a foot spindle being threadedly engaged with said threaded vertical bore and carrying a ground-engageable foot. On lowering of the foot by rotation of the foot spindle, the associated castor wheels can be jacked clear of the ground.
Whilst the foregoing exemplary castor assembly provides a relatively cost-effective castor assembly with integral jacking foot, we now consider that it would be advantageous to try to arrange the vertical axis of the foot to coincide substantially with the vertical axis of the castor pivot, in order to reduce the risk of the housing slewing sideways under the influence of a lateral force when the wheels are jacked clear of the ground.
However it is also desirable that the cost of the castor assembly be kept to a minimum since once the housing has been brought to its position of use, the castor wheels may not often be utilised again and, in effect, the provision of castor assemblies adds to the overall cost of the housing.
There is therefore a need for a castor assembly which incorporates a height adjustable jacking foot acting substantially on the pivotal axis of the castor assembly, but which is of inexpensive construction yet can be made relatively sturdy.
According to one aspect of the present invention we provide a castor assembly comprising a stem which is adapted at the upper end thereof to be connected to the base of a structure to be supported, a foot, a castor body swivellably mounted on the stem, a castor wheel carried by the castor body, the rotational axis of the castor wheel being offset from the axis of the stem to provide castoring, and a thrust bearing positioned at the upper end of the castor body, characterised in that the foot is carried by the lower end of the stem, the stem is adapted to be adjustably threadedly engaged with a threaded bore in said base whereby adjustment of the stem upper end causes the foot to be raised or lowered relative to the base, the castor body is arranged to be capable of vertical movement relative to the stem, and the thrust bearing is arranged to bear the vertical load acting between the castor body and the base when the foot is lifted clear of the floor and the castor wheel is supporting the structure.
Thus the foot is capable of being lowered or raised by screwing of the stem relative to the base. When the foot is lowered sufficiently relative the base the foot will support the load, but when the foot is raised sufficiently, the castor wheel Will then support the load.
It will be appreciated that the stem performs several functions:
i. It provides the means of attachment of the castor assembly to the base,
ii. it provides the means of adjustably supporting the foot whereby the foot can be raised and lowered relative to the base of the supported structure, and
iii. it acts to locate the swivellable castor body.
The various functions performed by the stem enable the overall cost of the castor assembly to be reduced.
A resilient means is preferably provided to bias the castor body upwards relative to the stem, thereby lifting the castor wheel clear of the floor when the foot is lowered sufficiently relative to the base.
A lock nut is preferably provided on the threaded upper part of the stem for locking engagement with the base of the structure, in order to lock the stem relative to the base when the required vertical adjustment of the stem has been achieved (usually when the housing has been fully supported by a plurality of the feet and has been brought to a horizontal attitude).
When a lock nut is provided then the thrust bearing can bear against the underside of the lock nut.
In order to resist tilting of the castor body about the vertical axis of the stem when the castor wheel is operative to support the load, the stem preferably carries adjacent to the foot a lateral bush which is located in a bore in the castor body.
Said castor body bore preferably houses a coiled compression spring which constitutes said resilient means.
The thrust bearing may simply be provided by a suitably hard upper surface of the castor body, but preferably the thrust bearing is a separate bearing assembly which may be a ball or needle-roller bearing assembly, but can be a plain bush.
In order to provide the necessary vertical adjustment of the stem relative to the base it will usually be necessary for the lower threads of the stem upper end to pass through the thrust bearing, and in order to avoid the possibility of the threads damaging the bearing, it may be desirable to provide a sleeve within the upper part of the castor body, to extend through the centre of the bearing.
When the thrust bearing is in the form of a plain bearing, the plain bearing can be dimensioned to act also as an upper lateral bush. Alternatively, when the thrust bearing is a ball or needle-roller bearing, an additional upper lateral bush may be provided adjacent to the thrust bearing in order to resist tilting of the castor body relative to the stem.
The invention, according to a second aspect thereof, comprises a housing comprising a housing base provided at each of a plurality of positions with castor assemblies in accordance with the first aspect of the invention.